In motorcycles, the brake and clutch are manually actuated by means of a lever device that is mounted on the handlebar of the motorcycle, a hydraulic tube or a Bowden cable extending therefrom to the system to be controlled, such as a brake or a clutch.
The lever of the lever device is usually arranged on the grip of the handlebar and the motorcyclist, in order to actuate the lever, grips the handlebar together with the lever and clenches the hand such as to rotate the lever towards the grip. The movement of the lever produces a thrust force acting on the hydraulic piston, the stroke or position thereof defining the fluid pressure inside said hydraulic pipe for the control of the brake or clutch. Upon actuation by means of a Bowden cable, the movement of the lever produces a traction force acting on the cable controlling the brake or clutch.
Since the different handlebars of motorcycles have different shapes and the motorcyclists' hands also have not the same shape and size, the need is felt to be able to adjust the rest position of the lever relative to the handlebar grip.
A number of various solutions have been suggested to provide an adjustment of the position of the lever. A group of these solutions provides an adjustment screw being screwed in a suitable threaded hole of the lever such that an end portion of the shank of the adjusting screw projects from the lever hole and abuts against a seat of the support structure of the lever device or against a transmission portion being interposed between the lever and the piston to be actuated.
By turning the adjusting screw, the length of its projecting portion, and hence the distance between the lever and said seat against which the adjusting screw abuts, can be changed.
In order to prevent that the adjusting screw may be accidentally and unvoluntarily rotated, for example both because of the vibrations of the motorcycle and a repeated actuation of the lever, it is known to provide locking devices for the screw, such as a nut or a ring nut being screwed on the adjusting screw and tightenable against the lever such that the threading of the adjusting screw is axially preloaded against that of the lever hole in order to increase the friction and accordingly the resistance against loosening of the screw.
This solution has proved to be not very reliable, particularly for sport motorcycles, which entail strong vibrations in use that are suitable to loosen the adjusting screw despite the locking ring nut.
Furthermore, the ring nut requires that a tool (nut wrench) be used for loosening and tightening the ring nut whenever the position of the lever requires to be adjusted.
A further solution envisaged by the inventor of the present invention provides an elastic plate placed between the head of the adjusting screw and the lever in order to provide either an elastic or snap locking of the adjusting screw in the selected position.
This solution would render the adjusting screw less sensitive to vibrations only when the screw head is sufficiently close to the lever to ensure a high preload of the elastic plate. This would entail either an undesired restriction of the adjusting stroke or an uneffective locking when the elastic plate is not sufficiently preloaded, i.e. pre-deformed.
The object of the present invention is therefore to provide an adjusting screw for control lever devices with adjusting lever having such characteristics as to overcome the drawbacks mentioned with reference to prior art as well as facilitating the assembly and maintenance of the adjusting screw.